1. Field of the Invention
The invention pertains to the field of variable camshaft timing (VCT) systems. More particularly, the invention pertains to a vane-type variable cam timing device employing worm trail reed valves to a flow of hydraulic fluid.
2. Description of Related Art
Engine performance in an engine having one or more camshafts can be improved, specifically in terms of idle quality, fuel economy, reduced emissions, or increased torque, by way of a variable cam timing (VCT) system. For example, the camshaft can be xe2x80x9cretardedxe2x80x9d for delayed closing of intake valves at idle for stability purposes and at high engine speed for enhanced output.
Likewise, the camshaft can be xe2x80x9cadvancedxe2x80x9d for premature closing of intake valves during mid-range operation to achieve higher volumetric efficiency with correspondingly higher levels of torque. In a dual-camshaft engine, retarding or advancing the camshaft is accomplished by changing the positional relationship of one of the camshafts, usually the camshaft that operates the intake valves of the engine, relative to the other camshaft and the crankshaft. Accordingly, retarding or advancing the camshaft varies the timing of the engine in terms of the operation of the intake valves relative to the exhaust valves, or in terms of the operation of the valves relative to the position of the crankshaft.
Many VCT systems incorporating hydraulics include an oscillatable rotor secured to a camshaft within an enclosed housing, where a chamber is defined between the rotor and housing. The rotor includes vanes mounted outwardly therefrom to divide the chamber into separated first and second fluid chambers. Such a VCT system often includes a fluid supplying configuration to transfer fluid within the housing from one side of a vane to the other, or vice versa, to thereby rotate the rotor with respect to the housing in one direction or the other. Such rotation is effective to advance or retard the position of the camshaft relative to the crankshaft. These VCT systems may either be xe2x80x9cself-poweredxe2x80x9d having a hydraulic system actuated in response to torque pulses flowing through the camshaft, or may be powered directly from oil pressure from an oil pump. Additionally, mechanical connecting devices are included to lock the rotor and housing in either a fully advanced or fully retarded position relative to one another.
Check valves are used to control the oil flow to the fluid chambers in the vanes. FIG. 5 shows a check valve (30) as known in the prior art. A base (31) forms the basic structure of the check valve (30). Seals (37), shown as o-rings in the figure, seal the check valve to prevent it from leaking. A disk (36) is located on the top of the base (31). The disk (36) is pushed up by oil flowing (34) through the base (31). A spring (38) is located above the base. A cap (35) covers the top of the base (31), the disk (36), and the spring (38). Oil can flow (34) only in one direction, up through the hole (33) at the bottom of the base (31).
The prior art valve is made up of multiple pieces, which makes it expensive to manufacture. Each of the pieces can separately wear out, subjecting it to durability concerns. In addition, the valve opens slowly, since it takes effort to unseat and lift the disk (36).
Therefore, there is a need in the art for a valve system which overcomes the disadvantages of the prior art.
The phaser of the present invention includes a reed plate. The reed plate has reed valves, which control the flow of hydraulic fluid. The reed valves are all inclusive on the reed plate. Worm trails in the surface of the parts sandwiching the reed plate direct the flow to and from the reed valves.